As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material. The packaging material has a multilayer structure comprising a layer of base material, e.g. paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material comprises a layer of oxygen-barrier material, e.g. aluminium foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
To open the above packages, various solutions have been proposed, a first one of which, described in U.S. Pat. No. 4,655,387 and U.S. Pat. No. 4,410,128, comprises forming, at the corner of a flap on the package, a preferential tear line defined by a succession of perforations extending through the outer layers of the packaging material down to the layer of barrier material. And the package is opened by lifting up the flap and cutting or tearing along the perforations. Once opened, packages of this sort, obviously, cannot be closed again, and must be handled with care, until all the food product is consumed, to prevent spillage of the product from the package.
To eliminate this drawback, the above packages have been fitted with reclosable opening devices, which substantially comprise a frame defining a through opening and applied to a hole or a pierceable or removable portion of a wall of the package; and a cap hinged to the frame. The cap is normally molded integrally with the frame, and is initially sealed to it, along a peripheral edge surrounding the opening, by a thin, breakable annular connecting portion. Once unsealed, the cap is movable between a closed position cooperating in fluidtight manner with the frame, and an open position.
Alternatively, threaded caps, separate from and initially screwed to the frame, are also used. In which case, the cap is normally molded integrally with a tamperproof ring connected coaxially to the cap by breakable radial connecting elements. More specifically, the cap is pressed onto the frame to click the tamperproof ring past the thread portion of the frame closest to the package; and, when the package is unsealed, the breakable connecting elements break off to detach the cap from the tamperproof ring, which remains where it is.
One problem of the opening devices described is that the cap must be removable from the frame or tamperproof ring with practically no effort when unsealing the package. For which purpose, the opening devices are made of easy-break plastic material, normally polyethylene.
Polyethylene, however, has the drawback of being a poor oxygen barrier. So, when the hole is formed through the full thickness of the packaging material, an additional cover element or “patch”, defined by a small sheet of heat-seal plastic material, must be applied over the hole on the side of the packaging material eventually forming the inside of the package; and the opposite side of the packaging material must be fitted with an oxygen-barrier element, e.g. a pull tab, which is heat sealed to the patch and comprises a layer of aluminium.
Fitting the package with a barrier element and patch, however, means additional work on the packaging material before it is sterilized and folded and sealed into a vertical tube, thus increasing the time and cost of producing the package.
Moreover, after unsealing the cap, the user also has to remove the barrier element for access to the contents of the package.
Alternatively, the hole may only be formed through the base layer of the packaging material, and is covered completely when the layers of heat-seal plastic material and barrier material are applied to the base layer.
In this case too, however, when unsealing the package, the user has to perform two successive operations: unseal the cap and either pierce or remove the material covering the hole in the base layer for access to the contents of the package.
Reclosable opening devices have therefore been proposed, designed to open the package in one operation, even when access to the contents of the package calls for piercing the packaging material.
In the solution described, for example, in international Patent Application WO 95/05996, opening devices of this sort substantially comprise a frame having a cylindrical collar defining a pour opening and fitted about a pierceable portion of the package; a removable cap screwed to the outside of the frame collar to close the pour opening; and a substantially tubular cylindrical cutter screwed inside the frame collar, and which cooperates with the pierceable portion of the package to detach it partly, i.e. with the exception of a small-angle flap, from the relative wall.
The cutter is activated by the cap by means of one-way ratchet-type transmission means, which are active when removing the cap from the collar. In the specific case described in the above international patent application, the cutter acts on the pierceable portion by means of an end edge parallel to the pierceable portion and having a number of teeth, all triangular and of the same height.
In actual use, the cutter moves spirally, with respect to the frame, from a raised rest position, in which the end teeth face the pierceable portion, into successive lowered cutting positions, in which the end teeth interact simultaneously with the pierceable portion.
One drawback of opening devices of the above type is that the teeth tend to “chew” the pierceable portion material, thus resulting in a jagged, frayed cut edge, the flaps of which tend to project through the pour opening and, at times, divert flow of the food product as it is poured out. Moreover, the cut-off part of the pierceable portion remains hanging inside the package, and, in use, tends to at least partly clog the flow section of the pour opening, thus seriously interfering with outflow of the product from the package.
To improve detachment of the pierceable portion from the rest of the packaging material, it has been proposed to make the cutter of more rigid material (e.g. polypropylene) than the frame and cap (normally made of polyethylene). This may result, however, in making the end teeth of the cutter overly fragile, thus resulting in potential breakage during transport and/or when unsealing the package, and dispersion of the teeth inside the food product.
To improve the efficiency of the cutter, various solutions have been proposed, the most significant would appear to be those described in Patent EP-B-1513732 and Patent Application US 2005/0242113.
More specifically, in the first of the above solutions, the cutter is guided, as it penetrates the wall of the package, so that its travel comprises a first purely vertical translation portion, and a second purely horizontal rotation portion.
In the second solution, the travel of the cutter, when unsealing the package, comprises a first spiraling portion, and a second purely horizontal rotation portion.
Though improving cutting quality of the pierceable portion from the rest of the packaging material, the above solutions are still not altogether satisfactory in achieving a clean cut with no frayed flaps projecting through the pour opening, and in solving the problem of the cut-off part of the pierceable portion interfering with pour-out of the product from the package.
Finally, it should be pointed out that the above limitations are particularly noticeable when the pierceable portion of the package is made of particularly tough material, e.g. a barrier material covered with a polymer catalyzed with an organometal or metallocene. In which case, the pierceable portion tends to “stretch” rather than tear under the action of the cutter, thus leaving threads on the cutter that may be passed on to the food product.